The invention relates to a manual control device for motorized displacements on three orthogonal axes of a machine element, such as the measuring head of a three-dimensional measuring machine.
Three types of three-dimensional measuring machines are currently known, namely manual displacement machines, motorized displacement machines, and motorized displacement, numerical-control machines.
Manual machines have the advantage of being very user-friendly and convenient to use since they are guided by the operator's hand. On the other hand they are slow because they use the same procedure consisting firstly of rapidly and manually displacing the various structural elements while performing what is conventionally referred to as the approach movement. Then, after stopping and locking each of these elements, causing each of the elements to advance by means of a micrometer screw until the measuring head contacts the part to be measured, the micrometer screw movement corresponding to a sensing movement.
This procedure provides very attractive levels of measurement precision, if only because the machine is at rest when sensing.
Skilled operators use these manual displacement machines to perform sensing on the fly, in other words, following the approach movement by the sensing movement. Under these conditions, they take the risk of damaging the electronic measuring head which is very expensive and especially of losing the benefit of the measuring accuracy since in the latter case they must take into account the considerable errors related to the dynamic defects in the mechanical structure of the machine. These defects are all the more difficult to overcome because they depend primarily on the more or less rough fashion in which the operator controls the machine.
Motorized machines, or those in which the displacements of the structural elements are produced by electric motors with a speed control, have the advantage of being slightly faster than manual machines, since they use on-the-fly sensing, while maintaining good measuring precision, since the forces required for displacement are always applied in the same way, and because it is possible to control the operating speed during sensing. The electric motors which produce the displacements of the structural elements are controlled by two optoelectronic or electromechanical levers, one of which is assigned to displacements in the horizontal plane and the other to displacements in the vertical plane. The manipulation of these two levers is not instinctive, making the maneuver difficult and imposing a psychological burden which distracts the operator from his measuring. Thus, it often happens that operators have no interest in this type of machine and prefer to use a numerical control machine which is much more expensive.
European Patent Application 23864 describes a manual control device in which the motorized element is controlled by electrical signals delivered by sensors detecting the deformations of deformable strips, the strips being crossed and actuated by a lever. Because of their structure, the deformable strips have a high flexural strength and an even greater torsional strength, making it necessary to provide expensive and complicated means to suppress the effect on the sensors produced by the parasitic forces on the control lever.
The stiffness of the device acts against its application to a three-dimensional measuring machine which requires control means whose operation must be flexible, gradual, and gentle, in order not to directly influence the motorized element and consequently the measurement precision.